Color filters for liquid crystal display apparatuses or the like include a red pixel portion (R), a green pixel portion (G), and a blue pixel portion (B). These pixel portions each have a structure in which a thin film composed of a synthetic resin containing an organic pigment dispersed therein is formed on a substrate. The organic pigment is an organic pigment for each of red, green, and blue colors.
In these pixel portions, a blue organic pigment for forming the blue pixel portion is generally an ε-copper phthalocyanine pigment (C.I. Pigment Blue 15:6). To adjust the color tone, a dioxazine violet pigment (C, I. Pigment Violet 23), which is a violet organic pigment, may be optionally used together in a small amount.
The organic pigment used when a color filter is produced needs to have characteristics totally different from those of organic pigments for general-purpose applications. Specifically, such an organic pigment needs to provide a brighter display screen of liquid crystal display apparatuses or the like (achieve higher luminance). However, if a dioxazine violet pigment is used together with an ε-copper phthalocyanine pigment, high brightness cannot be achieved. Therefore, achievement of higher brightness is particularly required for an organic pigment used for forming the blue pixel, portion (B).
In recent years, it has been considered that a triarylmethane pigment such as C.I. Pigment Blue 1, which is better than the ε-copper phthalocyanine pigment in terms of brightness, is used to form a blue pixel portion of a color filter to achieve higher brightness (PTLs 1 to 3).
A fanal color (FANAL BLUE D6340 and D6390) having the following chemical structure and manufactured by BASF is well-known as C. I. Pigment Blue 1. C. I. Pigment Blue 1 is obtained by forming. Victoria Pure Blue BO, which is a basic triarylmethane dye, into a lake with a heteropoly acid such as phosphomolybdate or phosphotungstomolybdate. In the thus-obtained C.I. Pigment Blue 1, the counterion X− of the cation is Keggin-type PMoxW12-xO40.
[Chem. 1]

[In general formula (II), R1, R2, and R3 are each an ethyl group; R4 is a hydrogen atom; and X− is a Keggin-type phosphotungstomolybdate anion or phosphomolybdate anion.]
When these triarylmethane pigments are used to form a blue pixel portion of a color filter, the light resistance can be maintained. However, satisfactory brightness still cannot be maintained for a long time at a high temperature of more than 200° C. As a matter of fact, the heat resistance is not sufficiently high.